Genotype-Selective Combination Therapies for Melanoma Identified by High-Throughput Drug Screening

Departments of 1Pathology and 2Dermatology, Yale University School of Medicine, New Haven, Connecticut.
Cancer Discovery (Impact Factor: 19.45). 12/2012; 3(1). DOI: 10.1158/2159-8290.CD-12-0408
Source: PubMed


Resistance and partial responses to targeted monotherapy are major obstacles in cancer treatment. Systematic approaches to identify efficacious drug combinations for cancer are not well established, especially in the context of genotype. To address this, we have tested pairwise combinations of an array of small-molecule inhibitors on early-passage melanoma cultures using combinatorial drug screening. Results reveal several inhibitor combinations effective for melanomas with activating RAS or BRAF mutations, including mutant BRAF melanomas with intrinsic or acquired resistance to vemurafenib. Inhibition of both EGF receptor and AKT sensitized treatment-resistant BRAF mutant melanoma cultures to vemurafenib. Melanomas with RAS mutations were more resistant to combination therapies relative to BRAF mutants, but were sensitive to combinations of statins and cyclin-dependent kinase inhibitors in vitro and in vivo. These results show the use of combinatorial drug screening for discovering unique treatment regimens that overcome resistance phenotypes of mutant BRAF- and RAS-driven melanomas.

We have used drug combinatorial screening to identify effective combinations for mutant BRAF melanomas, including those resistant to vemurafenib, and mutant RAS melanomas that are resistant to many therapies. Mechanisms governing the interactions of the drug combinations are proposed, and in vivo xenografts show the enhanced benefit and tolerability of a mutant RAS -selective combination, which is currently lacking in the clinic.

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    • "The application of phenotypic drug combination screening is exemplified by dose-ratio matrix testing multiple pairwise combinations across cell based assays enabling analysis of synergy, additive, and antagonistic effects across diverse chemical libraries, annotated compound libraries and approved drug sets (Zimmermann et al., 2007). Recent examples of dedicated drug combination screening campaigns using a variety of phenotypic assays and distinct endpoints have been published (Axelrod et al., 2013; Cubitt et al., 2013; Du et al., 2013; Held et al., 2013; Schmidt et al., 2013; Li et al., 2014). Such phenotypic screens have identified novel synergistic combinations such as: Lapatanib (EGFR and Her2 inhibitor) combined with the multi-targeted inhibitor Ro31-8220 (Axelrod et al., 2013); Lapatanib combined with MK2206 (Akt inhibitor) (Held et al., 2013) and Rapamycin (mTOR) combined with Sunitinib (multi-targeted kinase inhibitor) (Li et al., 2014). "
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    • "Dasatinib, an inhibitor of BCR-Abl kinase and SRC kinase, exhibited synergistic growth inhibition with afatinib in NSCLC lines expressing L858R/T790M or the combination of del E746-A750 with a deletion of exon 9 in PTEN (Chang and Wang 2012). In BRAF mutant melanoma cell lines, afatinib also had a little effect as a single agent but became a more potent growth inhibitor in the presence of Akt inhibitors (GSK690693 and MK-2206) (Held et al. 2013). Pfeifer and colleagues have systematically explored the compound combination PI-103 (dual PI3K/mTOR inhibitor) with afatinib on a panel of 65 NSCLC cell lines (Pfeifer et al. 2010). "
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    • "Many combination therapies are used to treat metastatic breast cancer [34]. Several inhibitor combinations effective for melanomas with activating RAS or BRAF mutations were recently discovered [35]. Combination therapy of α-galactosylceramide and 5-fluorouracil showed antitumor effect in mice and suggests a new therapy mode against metastatic liver cancer [36]. "
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